49 research outputs found
Gravitational Lensing by Asymptotically Flat Wormholes
Natural wormholes and its astrophysical signatures have been sugested in
various oportunities. By applying the strong field limit of gravitational
lensing theory, we calculate the deflection angle and magnification curves
produced by Morris-Thorne wormholes in asimptotically flat space-times. The
results show that wormholes act like convergent lenses. Therefore, we show that
it is hard to distinguish them from black holes using the deflection's angle of
the gravitational lens effect, in contrast with the results reported by Cramer
et.al. and Safanova et.al. However, we also show that it is possible, in
principle, distinguish them by the magnification curves, in particular, by
observing the position of the peak of the Einstein's ring.Comment: 9 pages, 14 figure
Detectores de partÃculas sobre variedades no minkowskianas
Se discuten los conceptos de vacÃo y partÃcula utilizando diferentes modelos de detectores y se comparan con aquellos derivados del método de segunda cuantización sobre variedades no Minkowskianas.The concepts of particle and vacuum are discussed using differents detector's models and are compared with those that arise from the second quantization method on a non-Minkowskian manifold
Can we distinguish between black holes and wormholes by their Einstein-ring systems?
For the last decade, the gravitational lensing in the strong gravitational
field has been studied eagerly. It is well known that, for the lensing by a
black hole, infinite number of Einstein rings are formed by the light rays
which wind around the black hole nearly on the photon sphere, which are called
relativistic Einstein rings. This is also the case for the lensing by a
wormhole. In this paper, we study the Einstein ring and relativistic Einstein
rings for the Schwarzschild black hole and the Ellis wormhole, the latter of
which is an example of traversable wormholes of the Morris-Thorne class. Given
the configuration of the gravitational lensing and the radii of the Einstein
ring and relativistic Einstein rings, we can distinguish between a black hole
and a wormhole in principle. We conclude that we can detect the relativistic
Einstein rings by wormholes which have the radii of the throat pc
at a galactic center with the distance 10Mpc and which have AU in
our galaxy using by the most powerful modern instruments which have the
resolution of arcsecond such as a 10-meter optical-infrared telescope.
The black holes which make the Einstein rings of the same size as the ones by
the wormholes are galactic supermassive black holes and the relativistic
Einstein rings by the black holes are too small to measure at this moment. We
may test some hypotheses of astrophysical wormholes by using the Einstein ring
and relativistic Einstein rings in the future.Comment: 13 pages, 2 figures, minor changes from v
Evolution of magnetic fields through cosmological perturbation theory
The origin of galactic and extra-galactic magnetic fields is an unsolved
problem in modern cosmology. A possible scenario comes from the idea of these
fields emerged from a small field, a seed, which was produced in the early
universe (phase transitions, inflation, ...) and it evolves in time.
Cosmological perturbation theory offers a natural way to study the evolution of
primordial magnetic fields. The dynamics for this field in the cosmological
context is described by a cosmic dynamo like equation, through the dynamo term.
In this paper we get the perturbed Maxwell's equations and compute the energy
momentum tensor to second order in perturbation theory in terms of gauge
invariant quantities. Two possible scenarios are discussed, first we consider a
FLRW background without magnetic field and we study the perturbation theory
introducing the magnetic field as a perturbation. The second scenario, we
consider a magnetized FLRW and build up the perturbation theory from this
background. We compare the cosmological dynamo like equation in both scenarios
Geodesic Deviation Equation in Bianchi Cosmologies
We present the Geodesic Deviation Equation (GDE) for the
Friedmann-Robertson-Walker(FRW) universe and we compare it with the equation
for Bianchi type I model. We justify consider this cosmological model due to
the recent importance the Bianchi Models have as alternative models in
cosmology. The main property of these models, solutions of Einstein Field
Equations (EFE) is that they are homogeneous as the FRW model but they are not
isotropic. We can see this because they have a non-null Weyl tensor in the GDE.Comment: Submitted to Journal of Physics: Conference Series (JPCS), ERE200
Noncommutative Geometry Inspired Rotating Black Hole in Three Dimensions
We find a new rotating black hole in three-dimensional anti-de Sitter space
using an anisotropic perfect fluid inspired by the noncommutative black hole.
We deduce the thermodynamical quantities of this black hole and compare them
with those of a rotating BTZ solution.Comment: 7 page
Boundary Term in Metric f(R) Gravity: Field Equations in the Metric Formalism
The main goal of this paper is to get in a straightforward form the field
equations in metric f(R) gravity, using elementary variational principles and
adding a boundary term in the action, instead of the usual treatment in an
equivalent scalar-tensor approach. We start with a brief review of the
Einstein-Hilbert action, together with the Gibbons-York-Hawking boundary term,
which is mentioned in some literature, but is generally missing. Next we
present in detail the field equations in metric f(R) gravity, including the
discussion about boundaries, and we compare with the Gibbons-York-Hawking term
in General Relativity. We notice that this boundary term is necessary in order
to have a well defined extremal action principle under metric variation.Comment: 12 pages, title changes by referee recommendation. Accepted for
publication in General Relativity and Gravitation. Matches with the accepted
versio